1. Field of the Invention
The invention pertains to the field of backlights for displays. More particularly, the invention pertains to backlight systems for liquid crystal (LCD) or other displays.
2. Description of Related Art
U.S. Pat. No. 5,410,345 “Stroboscopic Illumination System for Video Displays” discloses a backlighting system for video displays. It uses a number of vertically oriented parallel light sources (such as fluorescent tubes) spaced behind a lenticular lens, which creates up to hundreds of images of the light sources on a diffuser situated behind an LCD. The light lines are spaced apart from each other and from the LCD such that, combined with information presented on the pixels of the LCD, they serve to produce two or more separate images which are visible from different regions of space called “viewing zones” situated in front of the display. A person sitting within certain areas in front of the display will have one eye in one viewing zone and the other eye in another. The images visible within the different viewing zones will be different perspective views of a 3D scenes, and the person will perceive and image with depth. The aforementioned patent is incorporated herein by reference.
A detailed description of the manner in which light lines and images displayed using the pixels of an LCD produce 3D images is explained in detail in U.S. Pat. No. 4,717,949 “Autostereoscopic Display with Illuminating Lines and Light Valve”, which is incorporated herein by reference.
For further discussion of multiview autostereoscopic 3D displays, and how the 3D effect is produced by means of light emitting lines which in turn produce multiple horizontally spaced viewing zones, and various possible configurations of such displays see U.S. Pat. Nos. 4,829,365 and 5,410,245, assigned to the same assignee as the present invention, and which are incorporated herein by reference.
In such displays a series of thin, vertical light emitting lines with dark space in between is generated behind the columns of pixel elements of an LCD. The light lines are spaced apart from one another and from the LCD at such distances that, to an observer situated near an optimum viewing plane at a certain distance in front of the LCD, the lines will be seen through only certain sets of pixel columns by one eye, and, due to the difference in eye position, through an entirely different set of pixel columns by the other eye. Only dark space will be seen behind the remaining columns from those positions. Each eye thus sees the image information displayed on different sets of columns.
Different perspective views of a scene are displayed on different columns such that each eye, seeing a different perspective of the scene, perceives an image with apparent depth. Furthermore, since different perspective views can be displayed on different columns, the image can be made to change perspective like a real scene would as the observer moves around and sees the light lines through different columns of pixels; i.e. the observer can look around behind objects etc.
A characteristic of systems as described in the U.S. Pat. Nos. 4,717,949, 4,829,365, and 5,410,345 is that in the multiview configurations, in which one light of light is produced for every N columns of pixels, the 3D images possess a total resolution that is 1/N times the resolution of the LCD that is used to display them, since the available pixels in the LCD must be split between the N different perspective views that make up the 3D image. Furthermore, the resolution lost in 3D mode is all lost in the horizontal direction. Given a 3D image made up of N perspective views, and given an LCD with X×Y resolution, the resolution of the 3D images perceived by the observer is (X/N)×Y. In a typical multiview display where N may be on the order of 5 to 9, this mismatch in resolution between horizontal and vertical produces on obvious and undesirable “looking through a picket fence” effect.
Given a number of perspective views N, the 2D images used to create the 3D image will have a total resolution of 1/N times the resolution of the LCD, because the pixels of the LCD must be divided between the N multiple images. It is desirable that the resolution loss N be divided between the horizontal and vertical directions, and furthermore, it appears to be most advantageous to divide it equally between the horizontal and vertical directions. In such a case picket fence effects are avoided.
Various autostereoscopic display vendors, in particular Phillips and X3D, have achieved this equal resolution loss in both directions by placing tilted optical elements in front of LCD or plasma displays. Phillips uses lenticular lenses; X3D uses stair step patterns of slits in an opaque barrier in combination with color filters. All of these displays use optical elements that are tilted at a 3:1 slope angle (3 down, 1 over), so each one passes in front of successive pixel elements in different rows of pixels along a diagonal of those elements, instead of along a single vertical column. Explanations of how these displays are constructed and how they operate are found in U.S. Pat. No. 6,064,424 (Phillips) and U.S. Pat. Nos. 7,046,271, and 7,321,343 (X3D).
Each pixel of an LCD typically consists of three separate elements, a red element, a green element, and a blue element. Each of these elements is typically three times as high as it is wide, so that the three together, side by side, make up a square pixel. Since the square pixels are typically arranged in straight vertical columns, all of the red, green, and blue elements in each column line up to form red, green, and blue stripes running from the top of the display to the bottom. Thus a slanted lenticular lens, like Phillips uses, or a slanted barrier and color filter pattern, as X3D uses, or slanted light lines, as is described in this disclosure, that are angled to pass in front of the corner points of a group of pixel elements situated along a diagonal, will have a slope angle of 3:1, that is, the line will travel three units down for every unit to the side. In other words, the lines or lenses will make angles of 18.435 degrees to the vertical.
Instead of arranging the picture information from the different perspective views on different columns of pixel elements, these types of displays arrange the information from different perspective views onto different diagonal lines of pixel elements.